(1) Field of the Invention
This invention relates to a wavelength conversion system, an optical integrated device and a wavelength conversion method.
(2) Description of the Related Art
As increase in speed and capacity of optical communication proceeds, an all-optical signal processing technique which involves no conversion of an optical signal into an electric signal to perform processing is demanded.
Thanks to the progress of wavelength division multiplexing (WDM) techniques in recent years, it is possible to fully use an entire wavelength bandwidth over several THz of silica glass optical fibers. In the WDM wherein individual ones of wavelengths of light transmit different information applied thereto, wavelength conversion for implementing prevention of wavelength conflict and exchange by wavelength routing between sub networks is an essentially required technique.
When it is tried to perform all-optical wavelength conversion, methods which utilize a non-linear medium (NLM) such as an optical fiber or a semiconductor are used frequently. Among the methods, a wavelength conversion method which uses a non-linear effect of a semiconductor optical amplifier (SOA) is studied actively because it allows miniaturization of a system and can provide a high non-linear effect with low power consumption.
All-optical wavelength conversion methods which use the SOA can be classified into those of the optical switch type which make use of cross gain modulation (XGM) or cross phase modulation (XPM) and those of the coherent type which use difference frequency generation (DFG) or four wave mixing (FWM).
Of the two methods, the wavelength conversion method of the coherent type is ready also for a modulation format such as, for example, differential phase shift keying (DPSK) because it can perform very high speed wavelength conversion due to its high non-linear responsibility and besides maintains phase information also after the wavelength conversion.
Where the wavelength conversion method which uses the DFG and the wavelength conversion method which uses the FWM are compared with each other, in the wavelength conversion method which uses the DFG which is a second-order non-linear effect, the distance between wavelengths of light which act with each other is greater than that in the conversion wavelength method which uses the FWM which makes use of a third-order non-linear effect. Therefore, the wavelength conversion method which uses the FWM is more advantageous from the point of view of the facility in establishment of phase matching.
It is to be noted that Japanese Patent Laid-Open No. 2000-250081 and Japanese Patent Laid-Open No. 2004-185021 were found through a prior art search conducted.